This invention relates to electronic musical instruments, and more particularly relates to such instruments employing a keyboard in order to simulate the sounds of non-keyboard instruments.
String instruments which are bowed, such as violins and cellos, have long been known for their singular qualities of expressiveness and tone color which have made them the premier instruments in western orchestras for hundreds of years. These instruments create many harmonics of each fundamental note played on them, and this characteristic, in large part, is responsible for their rich tone color or timbre. Excitement is added by the fact that the tone color or timbre of these instruments changes as they are played. Even minute changes in the bowing pressure, rate, and attack angle, as well as the pressure and position of the fingers on the finger board of the instruments, create differences in the intensity and identity of the harmonics. As a result, the harmonics of a single bowed instrument change in a complex way, and the harmonics of multiple bowed instruments played simultaneously involve random and complicated changes which defy mathematical analysis.
Multiple bowed instruments often are played simultaneously in order to form a string chorus. The blending of the sounds of the multiple instruments in the chorus creates an audible sensation which is qualitatively different from the sound of a solo instrument. The variations in sound created by the eccentricities of the individual players of the chorus combine to form a rich sonority which is pleasing to the ear.
Since the sound of a string chorus requires a performance by many skilled and dedicated musicians, it is an expensive art form which is generally reserved for a concert stage. Because of the expense and difficulty of obtaining a string chorus sound with natural acoustical instruments and musicians, it is highly desirable to design an electronic musical instrument which can simulate this sound.
Accordingly, it is a primary object of the present invention to provide an electronic musical instrument which simulates the sound of a string chorus.
Another object of the present invention is to provide an electronic musical instrument playable by a keyboard which simulates the sound of a string chorus.
Still another object of the present invention is to provide an electronic musical instrument of the foregoing type in which the fundamental pitch of the tone being produced can be accurately maintained over a long period of time.
It has been surprisingly discovered that the foregoing objects can be achieved by simultaneously generating in connection with each of the keys of the instrument first and second electrical tone signals which have a particular relationship to each other. The first tone signal is generated at a first repetition rate which is frequency modulated. That is, the first repetition rate has a value which oscillates at a modulation frequency around a center rate. The second electrical tone signal has a waveshape which deviates from the waveshape of the first electrical tone signal either statically or dynamically. In addition, the second electrical tone signal has a repetition rate which is different from the center rate of the first electrical tone signal. In response to the actuation of the keys, the first and second electrical tone signals are mixed and converted to corresponding acoustical waves in order to produce the sound of a string chorus. Since pairs of first and second electrical tone signals are produced for each of the keys, several of the keys can be actuated at once to play chords which further enhance the string chorus effect.
Another feature of the present invention can be used in connection with electronic musical instruments having a keyboard including twelve keys corresponding to the twelve notes of a chromatic musical scale. Circuitry simultaneously generates a first series of twelve tone signals corresponding to a first tempered scale and a second series of twelve tone signals corresponding to a different second tempered scale. A pair of tone signals, one from each of the first and second series, corresponds to each of the keys. When a key is actuated, the tone signals from the first and second series tuned according to the different tempered scales are mixed and converted to an acoustical wave which simulates the sound of a string chorus.
The first and second features of the invention also can be combined in order to enhance the string chorus effect.
According to a third aspect of the invention, the notes of an electronic musical instrument having a keyboard by which the notes are played can be kept in tune by providing a high frequency oscillator which generates clock pulses that are divided in time in order to form tone pulse waveforms corresponding in pitch to the various keys. A low frequency oscillator generates timing pulses corresponding to the pitch of one of the tone pulse waveforms. A comparator compares the phase of the timing pulses with the predetermined one of the tone pulse waveforms and generates a correction signal which varies the repetition rate of the high frequency oscillator so that the notes remain in tune.
By using the foregoing techniques, it has been discovered that the sound of a string chorus can be simulated with a degree of ease and accuracy heretofore unattainable, and that the instrument can be kept in accurate tone over long periods of time.